This invention relates to a hydraulic snubber and more particularly, to a hydraulic snubber especially advantageous in connecting the head assembly of a grapple to the boom mount such as are found on the rear frame of crawler or rubber-tired tractor skidders.
A grapple with which the invention can be used advantageously is seen in my earlier U.S. Pat. No. 4,358,147 and a skidding grapple is seen in co-owned U.S. Pat. No. 4,400,132.
Uneven ground and rapid changes in speed and direction of the skidder cause the empty grapple head assembly to swing violently when unrestrained. This swinging motion causes the grapple head to bang into the boom and rear frame of the skidder, resulting in damage to the boom, grapple and tractor.
The purpose of the snubber, which is the connecting link between the grapple head and boom, is to dampen the violent damage-causing motion out. At the same time, the snubber link, being a universal type joint, must allow controlled movement of up to 90 degrees each side of plumb in the lateral and longitudinal direction relative to the tractor.
Current means of dampening this motion are subject to high maintenance and frequent adjustments in order to perform well with consistency and are rendered useless when contaminated with oil or grease. The inventive snubber described here requires no adjustment and infrequent maintenance. It is a sealed unit, has only two moving parts, and works on the known principle of force induced fluid displacement (see U.S. Pat. No. 3,592,503). Grease or other high viscosity synthetic lubricant is contained in two cylindrical chambers, divided into two inversely variable compartments.
Two diametrically opposed vanes cause the chamber division. One vane is integral with a rotatable housing, and the other with a rotor which is in turn keyed to a fixed pin (or the opposite may be the case). Chamber compartment volumes vary inversely as one vane is rotated relative to the other. This variation in volume causes the dampening medium to be forced from one compartment to the other across the vanes. The passage or area through which the dampening medium must cross is such that it restricts free flow and creates a pressure drop across the vanes so that free rotation is restricted. This effect is true with rotation in either direction.
According to the invention, a novel construction of snubber is provided which makes possible universal joint action and further a vane extension configuration is provided that adjustably responds to pressure changes so as to achieve a desired snubbing or shock absorbing action.
Other objects and advantages of the invention may be seen in the details of the ensuing specification.